yes ericaceous compost. I would do it now, the plant looks well established in the pot, check that its not root bound i.e the roots tightly bound in the pot and if they are going around they will keep going around even when in the ground and it will never eatablish properly eventually falling over, so cut the roots with a sharp knife.
Remove the plant from the pot and slash the roots in three different locations around the root ball this will stimulate fuberous roots which will grow out into the surrounding soil.

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